Axial piston pump or motor device



nited States Patent 72] lnventor Robert J. Martin Hutchinson, Kansas [211 App]. No. 753,560

{22] Filed Aug. 19, 1968 [45] Patented Dec. 1, 1970 {73] Assignee The Cessna Aircratt Company Wichita, Kansas a corporation of Kansas I [54] AXIAL PISTON PUMP 0R MOTOR DEVICE 7 Claims, 3 Drawing Figs.

[52] 11.8. C1 91/507 [51] Int. Cl F04b 1/02,

FOlb 13/04, [50] Field ofSearch 103/162;

[56] References Cited UNITED STATES PATENTS 2,776,628 [/1957 Keel 103/162 2,953,099 9/1960 Budzich 103/162 3,191,543 6/1965 Hann et al. 103/162 3,241,495 3/1966 Diedrich et al.. 103/162 3,292,553 12/1966 Hann 103/162 3,304,885 2/1967 Orth 103/162 Primary Examiner-William L. Freeh Attorneys-Gregory J. Nelson and Hubert E. Miller ABSTRACT: An axial piston-type hydraulic pump or motor in which the cylinder block is mounted in the housing for selective adjustment during assembly to insure sealing engagement with the mating backplate surface during operation. The cylinder block is supportingly engaged by abutment means on the drive shaft to limit axial separation of the cylinder block away from the backplate to a predetermined maximum clearance. Selective adjustment is achieved through means which vary the effective axial position of the shaft abutment means.

Patentd Dec. 1, 1970 3,543,649

Sheet 1 of3 FIG I I INVENTOR. ROBERT J. MARTIN Patented Dec. 1, 1970 I Sheet 2 of 3 INVENTOR. ROBERT J. MARTIN ATTORNEY Sheet INVENTOR. ROBERT J. MARTIN TTORNEY AXIAL PISTON PUMP OR MOTOR DEVICE AXIAL PISTON PUMP OR MOTOR DEVICE This invention pertains to fluid power devices of the axial type having reciprocating pistonsJMore specifically, the invention relates to the maintaining of sealing clearance by limiting axial separation of the cylinder block and the mating backplate in axial piston-type hydraulic pumps and motors without utilizing biasing means.

Fluid power devices, pumps and motors, of the reciprocating axial piston-type are well known and consist mainly of a rotary cylinder block drivingly affixed to a shaft and having a concentric ring of cylinder bores spaced about the axis of the shaft with pistons disposed for reciprocation therein. The outer ends of the pistons are formed as spherical bearings to which are swaged flanged shoes having a bearing face. Rotative about an axially movable spherical collar affixed to the shaft is a spider plate which engages the socketed piston shoes. An inclined or inclinable thrust or swashplate bears against the bearing face of the flanged shoes to receive or to transmit force to or from the pistons upon rotation of the block and pistons. A stationary baclcpl'ate mates with the face of the cylinder block and provides properly phased inlet and outlet passages communicating through ports in the block with each cylinder upon relative rotation of the block. The term backplate as used herein refers to the plate which is secured to the housing and mates with the cylinder block in known manner to successively connect the cylinder ports and inlet and outlet passages upon rotation of the cylinder block. In some cases, a valve plate or port plate may be interposed between the backplate and cylinder vblock. Although the drawings do not show a valve plate, as the backplate serves this function, it is to be understood that one could be included in the unit.

When a pump or motor unit of this general type is operating under pressure, the cylinderblock is positively urged against the backplate by hydraulic pressure forces due to the design of the mating surfaces of the cylinder block and backplate. However, when the unit is operating under zero pressure and during start-up, these pressure forces are not present to maintain intimate contact between the cylinder block and backplate, allowing excessive leakage of hydraulic fluid resulting in loss of pressure and loss of efficiency.

Similarly, to prevent lifting off and accompanying leakage and loss of efficiency, the piston shoe bearing surfaces which rotate against the swashplate must be positively biased against the swashplate, particularly during the suction portion of the cycle. Thus, it becomes necessary to provide means which ensure contact between the cylinder block and backplate faces as well as maintaining contact between the piston shoes and the swashplate.

Several schemes for mechanically constraining the rotating parts together can be found in the prior art. The simplest of these provides a spring or a series of springs positioned within a central recess in the cylinder block. One end of the spring acts against the cylinder block through a snap ring in the cylinder block and the other end is exerted against the spherical collar through axial push rods extending in bores in the block. This scheme is effective to bias both the cylinder block against the valve plate and the pistons outwardly against the swashplate; however, it is disadvantageous in that the same spring force acts in both directions, as it has been discovered that, in some cases, the force necessary to maintain the pistons in contact with the swashplate is much greater than the force necessary to maintain engagement between the cylinder block and backplate. In an attempt to achieve a more acceptable design, the use of two separate springs has been proposed. In this latter arrangement, a first coil spring disposed about the drive shaft engages a grounded abutment, such as a collar on the shaft, and acts against the cylinder block through a snapring arrangement. Second spring means, also acting against the abutment exerts a spring force against the spherical collar biasing the pistons. The first and second springs act independently in opposite directions and are both grounded to the shaft at the common abutment. This latter scheme, while overcoming some of the objections of other prior art devices employing springs, presents difficult problems of assembly and disassembly. Moreover, all of these prior art designs have the common disadvantage that due to the biasing force applied to the cylinder block, friction and drag during start-up and zero pressure operation is substantial. This, it will be appreciated, necessitates high starting torque in pump units, increases wear, and reduces starting output torque of axial motor units.

Thus, it can be clearly seen that there is a need for an improved construction which maintains the sealing clearance between the cylinder block and backplate in hydraulic axial pumps and motors while eliminating attendant drag and friction problems.

Accordingly, it is a principal object of the invention to provide an improved means in a fluid pump or motor for maintaining sealing tolerance between the cylinder block and the valve plate.

It is a more specific object of the present invention to provide a fluid pump or motor in which force transmitting means act to transfer a biasing force to urge the pistons onto the swashplate and whereby the proper sealing clearance between the cylinder block and backplate is insured by provision of an adjustment mechanism which allows precise positioning of the cylinder block within the housing.

Another object of this invention is to provide in an axial piston hydraulic unit a means of adjusting the relationship of the cylinder block to its mating backplate surface, eliminating the need for spring loading of the cylinder block onto the backplate.

A more particular object of this invention is to provide a means for limiting the axial separation of the cylinder block and backplate components in an axial piston unit by abutment means on the shaft engaging the block, the effective axial position of the shaft abutment being selectively adjustable.

Another object of this invention is to provide an axial fluid device in which the cylinder block is adjustably constrained from axial movement in one direction but is free to follow deflections of the backplate in the other to insure proper sealing at all operating conditions.

Another object is to provide an improved axial fluid device which facilitates assembly and disassembly, both in the shop and field.

Briefly, according to the invention, an axial piston hydraulic device of the type heretofore described is provided with a central recess in the cylinder block around the drive shaft. Biasing means, as for example a spring transmitting force through pins in bores in the cylinder block, act against an adjustable sleeve and engage the spherical collar slidably splined to the shaft to urge the piston shoes into engagement with the swashplate. An abutment is provided on the drive shaft which acts to effectively engage the cylinder block in a predetermined position in cooperation with an abutment in the cylinder block within the recess. Axial adjustment of the cylinder block in relation to the unit body is achieved by moving the effective position of the abutment on this shaft. This may be done, for example, by shims or by the abutment itself being provided with means for adjustability.

Thus, the pistons are positively biased against the swashplate, and the cylinder block may be precisely positioned with respect to the backplate without the necessity of a continuous biasing force urging the cylinder block against the backplate. The present invention will be more completely understood and further objects and'advantages of the present invention will be apparent to those skilled in the art, from the following description of the invention taken in conjunction with the drawings in which:

FIG. I is a longitudinal sectional view of the hydraulic device constructed in accordance with the invention;

FIG. 2 is a longitudinal sectional view of another embodiment incorporating the present invention; and

FIG. 3 is an enlarged detail view of a portion of FIG. 1 with maximum axial separation of the cylinder block from the backplate being shown in exaggerated proportion.

Referring to FIG. 1, a pump or motor is generally indicated at it), having a housing 11 and backplate 13 defining a central cavity 12. Shaft bearing 14 is pressed into the end of housing 1 1. Drive shaft 15, which is rotatable by means not shown, extends through bearing 14 and terminates in bearing 16, which is mounted in end plate 13. The main shaft bearings 14 and 16 support shaft for rotation within the housing and are designed to accommodate the radial and axial thrust loadings occurring during operation of the unit.

Within the cavity 12 of housing 11, cylinder block 20 is rotatably connected by axial splines 21. on shaft 15 cooperating with loose fitting grooves 22 in the cylinder block. This splined connection allows relative axial movement of cylinder block 20 with respect to shaft 15, as well as providing some compensation for angular misalinement of the parts. Annular bores 23 equally spaced and radially disposed about the axis of shaft 15 accommodate pistons 24 which are formed having spherical outer ends 25. Flanged piston shoes 26 are swaged onto piston ends 25 to allow universal movement. Spider plate engages the shoes 26 and carries the shoes for slidable engagement with swashplate 33. Spider 30 is secured for pivotal movement at its center to spherical collar 31 which is also cooperatively splined to shaft splines 21 at grooves 32 for slidable movement along shaft 15.

Swash or thrust plate 33 contacts the bearing faces of piston shoes 26 and is inclinable in trunnions, not shown, mounted in housing 11. As is well known in the art, the inclination of the swashplate controls the stroke of the pistons and, accordingly, the displacement and operating pressure of the unit during relative rotation of the cylinder block.

Backplate 13, having a face 38 of specially hardened material, has ports 36 which serve as fluid inlets and outlets in hydraulic communication with the cylinder ports 37. These ports place cylinder bores 23 in the proper phase through ports 37 during rotation of the cylinder block.

Referring now to both FIGS. 1 and 3, cylinder block 20 is designed having an annular recess 40 around shaft 15 in the end of the block adjacent backplate 13. Within recess 40, biasing means 41 such as a coil spring axially encircles shaft 15 and exerts a force to bias spider collar 30 toward the swashplate. The force of the spring is transmitted to collar 30 through a mechanical connection comprising washer 42 and push rods 43 which extend through holes provided in the cylinder block. The opposite end of spring 41 is grounded or anchored to shaft 15 by adjustable sleeve 45 which is screwed to the shaft on threads 46. Sleeve 45 is flanged having radial projection against which washer 47 seats through the force of spring 41. Radial projection 50 is provided with slots 51 in its outer face to accommodate the blade of a tool for installation and axial adjustment of sleeve 45. Snapring 48 completes the assembly and engages snapring groove 49 in cylinder body 20 within the recess 40. The inner edge of washer 47 abuts against the rear side of flange 50 and transfers the force of spring 41 to the shaft through sleeve 45 while the outer edge of washer 47 acts to engage snapring 48 to limit axial movement of the cylinder block toward the swashplate.

Central recess 40 is shown as having a nonuniform cross section as more fully described in my copending U.S. Pat. application Ser. No. 747,877, entitled Pump or Motor Device, filed July 26, 1968, now U.S. Pat. No. 3,522,759. In this particular design the central recess is provided with one or more peripheral grooves which allow rod 43 to be radially spaced apart a sufficient distance from the splined connection 22 to provide adequate material strength in the neck of the cylinder block.

Thus, in assembly this unit,-push rods 43 are placed in the holes in the cylinder block and washer 42 and spring 41 are placed within recess 41) in cylinder block 20. The second washer 47 is inserted over shaft 15 and sleeve 45 is screwed onto threads 46, thereby compressing spring 41 and loading the piston shoes onto the swashplate. Snapring 4% is then inserted in groove 49in cylinder block 249 and the unit is turned upright. The axial separation of cylinder block 26 from the backplate is limited by the effective position of collar flange 50 acting through spring retained washer 47 and snapring 43.

Sleeve 45 is manually adjusted by advancement on threads 46 until the precise predetermined running clearance between face 38 of the backplate 13 and the face 19 of the cylinder block 20 is set. It can be seen face 38 of the backplate is fixed with reference to face 18 of housing 11, whereas the position of face 19 of the cylinder block is variable depending on the axial position of abutment 50. Cylinder block 21) may be adjusted so that line-to-line contact exists between mating faces 19 and 38 or a few thousandths of an inch clearance may be allowed if desired. Fig. 3 illustrates the maximum separation between surfaces 38 and 19 allowed by the constraining means in exaggerated proportions for clarity. The axial position of collar 45 preset during assembly is maintained during operation by friction holding means. For example, plastic retaining compound may be applied to the mating threads or the threads or sleeve may be mechanically deformed to insure tightness.

End plate 13 is bolted onto body 12 completing the assembly. The adjustment of face 19 with respect to face 18 has assured the proper clearance between faces 19 and 38. it is obvious that cylinder block 20 can be precisely positioned with respect to backplate surface 38 by adjustment of sleeve 45 without using a biasing force urging cylinder block onto the backplate. As is apparent in FIG. 3, cylinder block 20 is free to move away from collar washer stop 47 and into contact with face 38 of the backplate in response to fluid pressure within bores 23. The axial movement away from face 38 is clearly limited by the position of collar 45. The absence of any mechanical biasing force acting on the cylinder block decreases friction losses and drag and increases pump efficien cy during start-up, low-pressure and all other operating pressure conditions. A gasket may be included during assembly between the backplate and housing to minimize fluid leakage and its width taken into consideration in adjusting sleeve 45.

It will be obvious to those skilled in the art to omit washer 47 and radially extend flange 50 to the periphery of recess 49 so that flange 50 acts directly to engage snapring 48. This modification of the invention, while acceptable to limit separation of the working elements, has certain disadvantages of adjustment and disassembly that make the FIG. I embodiment preferable.

Turning now to FIG. 2, another preferred embodiment is illustrated. In this embodiment a piston pump or motor unit If) is constructed as the device of FIG. 1; however, the means provided for adjusting the axial position of cylinder block 20 are slightly modified, as well as the means for biasing the pistons against the swashplate.

In this embodiment, adjustability of the axial position of the cylinder block is achieved by shimming against a fixed abutment on the drive shaft. A fixed collar 60, shown as a snapring, is secured to shaft 61 within the recess in cylinder block 20. Snapring 65 is provided in the cylinder block. Encircling drive shaft 61 and abutting snaprings 65 and 60, respectively, are washers 64 and 62. Interposed between washers 64 and 62 are shims 63. It will be seen that the cylinder block is prevented from axial movement toward the swashplate. Snapring 65 in the cylinder block abuts washer 64 which in turn, through shims 63 and washer 62, abuts snapring 60.

Also, in the present embodiment, the force to hold down the piston shoes is exerted by compression springs 71 arranged in annular bores in cylinder block Ztl. The springs 71 extend between snapring 68 on shaft 61 and spherical collar 75. In this embodiment spherical collar 75 is shown as having an extended flanged portion against which the springs seat.

Bores 71 which accommodate the biasing springs are shown as being angularly disposed in the cylinder block for compactness and cylinder wall strength, but may be bored parallel to the shaft axis.

With the present design adjustment of the axial position of the cylinder is accomplished by placing a predetermined thickness of shims 62 between washers 62 and 64. Varying the stack height of shims 62 will change the maximum operating clearance between mating faces '19 and 38, this clearance being preset during assembly of the unit components. During operation of the unit, the cylinder is not restrained from axial movement toward the end plate, ,but is free to deflect therewith as in the FIG. 1 embodiment.

The utilization of the present invention obviates the necessity of biasing the cylinder block on the backplate by mechanical means. Mechanical force transmitting means act only to bias the cylinder shoes against the swashplate. Cylinder block is constrained, by the supporting engagement of the abutment on the shaft, from axial movement in the direction of the swashplate while remaining free to follow deflections of the backplate to maintain at all operating conditions intimate contact between cylinder block and backplate. The restriction on bidirectional movement along with preadjustment of the relationship of the mating cylinder and backplate surfaces assures that sealing will be achieved automatically during operation by the sizing and positioning of bearing areas of the mating surfaces.

The zero bias on the cylinder block decreases friction and drag and increases overall unit efficiency. Further, the required starting torque is reduced by use of the present invention. In motors starting output torque is increased.

Another advantage of the present invention is that field disassembly of the unit is facilitated as special press loading equipment is not required for rem-oval of the components within the cylinder block recess.

It will be obvious to those skilled in the art to make various modifications to the invention herein disclosed; however, to the extent that such modifications and changes do not depart from the spirit of the invention, they are intended to be included in the scope thereof, which is not limited to the embodiments specifically illustrated in the drawings but rather only by ajust and fair interpretation ofthe claims.

I claim:

1. In an axial piston hydraulic device including a housing, a shaft rotatable within said housing, a cylinder block having a plurality of axial cylinder bores spaced about the shaft and having associated ports communicating with said bores, a driving connection between said cylinder block and said shaft, said connection allowing for axial adjustment of the cylinder block, a backplate affixed to the housing, said backplate mating with the cylinder block providing properly phased fluid inlet and outlet connections to each cylinder port upon rotation of the cylinder block, pistons having their inner ends disposed within the cylinder bores for reciprocation therein, a spherical collar axially slidable on said shaft, holddown means engaging the outer ends of the pistons, said holddown means being engaged by the slidable collar for pivotal movement about the collar, an inclinable swashplate positioned to operably reciprocate the pistons upon rotation of the cylinder block, means for biasing the pistons toward the swash plate, wherein the improvement comprises:

cylinder block constraining means providing free axial movement of the cylinder block adjacent the backplate while constraining the cylinder block to a predetermined maximum separation from the backplate, said constraining means including first abutment means on the cylinder block, and second abutment means on the shaft positioned to effectively engage the first abutment means only at said predetermined maximum separation.

2. An axial piston hydraulic device including a housing, a shaft rotatable within said housing, a cylinder block splined to said shaft for rotation with the shaft and defining a central recess surrounding said shaft, said cylinder block having a plurality of axial cylinder bores spaced about the shaft and having associated ports communicating with said bores, a backplate affixed to the housing, said backplate mating with the cylinder block and providing properly phasedinlet and outlet connections to each cylinder port upon rotation of the cylinder block,

pistons having their inner ends disposed within the cylinder bores for reciprocation therein, a spherical collar axially slidable on said shaft, holddown means engaging the outer ends of the pistons, said holddown means being engaged by the spherical collar for pivotal movement about the collar, an inclinable swashplate positioned to operably reciprocate the pistons upon rotation of the cylinder block, wherein the improvement comprises:

an adjustable sleeve having a radially projecting flange, said sleeve being in threaded engagement with the shaft to provide axial adjustability;

abutment means located within said central recess in said cylinder block;

a push rod extending from said recess through a bore in the cylinder block to contact said collar; and

spring means acting between said push rod and said flange and acting to engage said abutment means to limit the axial separation of the cylinder block from said backplate without biasing the cylinder block toward said backplate.

3. The apparatus of claim 2 wherein a washer encircling the shaft is interposed between said spring means and said flange to engage said abutment means.

4. An axial piston hydraulic device including a housing, a shaft rotatable within said housing, a cylinder block splined to said shaft for rotation with the shaft, said cylinder block having a plurality of axial cylinder bores spaced about the shaft and having associated ports communicating with said bores, a backplate affixed to the housing, said backplate mating with the cylinder block and providing properly phased inlet and outlet connections to each cylinder port upon rotation of the cylinder block, pistons having their inner ends disposed within the cylinder bores for reciprocation therein, a spherical collar axially slidable on said shaft, holddown means connected to the outer ends of the pistons, said holddown means being engaged by the spherical collar for pivotal movement about the collar, an inclinable swashplate positioned to operably reciprocate the pistons upon rotation of the cylinder block, wherein the improvement comprises:

biasing means grounded to said shaft acting against the spherical collar to hold down the pistons;

first abutment means in said cylinder block;

second abutment means on said shaft axially spaced apart toward the swashplate from said first abutment means; and

axially rigid adjusting means interposed between said first and second abutment means providing free axial movement of the cylinder block adjacent the backplate while constraining the cylinder block to a predetermined maximum separation from the backplate, said rigid means being axially adjustable to vary said maximum separation.

5. The apparatus of claim 4 wherein said adjusting means for varying said maximum separation comprises a washer encircling the shaft and at least one shim interposed between said washer and one of said abutments.

6. The apparatus of claim 4 wherein said biasing means comprises spring means disposed in bores in the cylinder block angular with respect to the shaft axis opening into a central recess of the cylinder block and grounded to the shaft by abutment means within said recess.

7. The apparatus of claim 1 provided with means for selectively adjusting the relative locations of said abutment means to establish said predetermined maximum separation. 

